How Do You Convert a Page-Based PHP Application to MVC?

since your boss is buzzword-happy, tell him to look up "refactor"

Slightly off topic to your question... for the love of god don't forget your old URLS. The reason being is that the minute you flip the switch on the new site and its pretty URLS, all of the aggregated content held by the search engines will slowly expire, taking your SEO stats way down.

UPDATE: If I try and stick with one controller per view...I will then be keeping code per request to a minimum, but is this the best way?

If I understand you correctly, each controller would produce one page. This can be a really bad idea that I've experienced first hand in a maintenance position. If you have content that doesn't really match well to the OO paradigms then put it into a category: press releases, one offs, informational, etc and stick those into a controller that serves just those views or better yet a number of controllers per category to leave more fine grained control.

The "MVC" framework I dealt with that did the one controller to view quickly became a convoluted mess with lots of hacks and spaghetti code.

I have about 12 form pages that are used to create a "plan".

I've had to do something similar and as goofy as it seems, having a "planningform" controller is probably best. Yes there are multiple tables to feed, but you can do simple stuff like $_SESSION['plannerController']['subject|action'][key][value] to keep each part of the form overall in check. Having each method handle part of the multi-page form can also be a benefit ( ex. What if your boss says they only need 6 out of the 12 pages or what if part 7 becomes really complicated and needs stuff like autocompletion ajax ).

grouping mechanism not necessarily using it because they have something related with each other.

I generally like the one class, one purpose paradigm but sometimes it just doesn't make sense to try and do that. There are cases where its clear cut, right out of the text book OO and other times the academic BS can go to hell. Your going to find stuff that doesn't fit the OO mold, so you can take a step back and try to merge things into common categories.

What is the point of having one view per controller?

Again:

1. You are not loading more code than is necessary per request. Would you load a library, package, dll, that you didn't require? Of course not. So don't create a massive controller file where only a small portion of the code will be executed per request. Also, smaller files are easier to maintain imo, just like smaller methods and modular code.
2. there is a clear 1:1 link between controller and view (especially if they share the same name). This is a convention. It's clear and consistent. If I am looking at a view template, I know exactly the controller that loads it based only on the file name. There is no thinking involved. No decisions. No compromises.

What need is there for a separation of concerns when everything is just pair matched?

What need is there for a separation of concerns? If you want to group related pages (controllers/views), lump them in directories.

I'd be more inclined to write a controller that controls several views that are related in some way. For instance, the aforementioned add/view/edit of a user. You'd want to keep similar functionality together rather than searching through many files for the code you want. It's also handy to have all the methods defined (for a particular object) in one place. Makes maintenance MUCH easier.

I'm going to respectfully disagree. If I have a single view that is responsible for adding/viewing/editing a user, then with the 1:1 convention I know exactly the controller responsible. On the other hand, using your suggestion of grouping similar functionality, if I have a manager controller and a user controller, which one contains the add/view/edit for a manager? User or manager? Now you have to think, or search.

I worked on a project using a PHP framework that created a separate file per 'action'. Named like 'object(action)' and it became a NIGHTMARE to maintain.

I'm not suggesting that.

I've been using Django for a little while now which keeps all the models in one file, all the views (controllers) in one file, and the templates (views) separately. [Django isn't MVC but for these purposes let's pretend it is]. This allows you to group together common code in one place and maintenance becomes much easier.

I'm feeling whoosy now. I don't know Django, and I'm assuming the single files are optional, but there is no way I'd maintain a file with tens of thousands of lines.

My only advice is - don't try to organise your project based on some ideal of MVC. Organise your project how it makes sense to you and your domain.

No, no, no. That is very dangerous advice. Design patterns, coding conventions, and frameworks were designed for a purpose - best practices and consistency. Only a guru should step outside conventions and only if he/she works alone. Even within the confines of a framework, I constantly strive for greater consistency so that I don't have to think when writing or maintaining the code.