Here’s a tell tale sign that you have product market fit - your product is buggy and sucks and your customers constantly complain and demand more improvement but they can’t give you up. They need to pay you because you serve a need they can’t or wont find somewhere else.
The customer needs a bespoke feature that really only they will use and isn’t general to anyone else? Is the founder team disciplined enough to say no and focus on what really adds value? Sure, they would love for you to be a cheap outsourced dev shop, but that’s why your CEO needs to push back and sell the vision of the company.
Phases 1, 2 and 3 are backwards. Why is the startup trying to be a consulting company? This doesn’t sound like the story of any visionary startup I know of. It sounds like a group of developers who can make a profitable software consulting company trying to pivot to making a product. IMHO a startup can be really dysfunctional in its dev process and management and still succeed, if they find product market fit first.