I am a full stack developer in a very small company.
It has a custom built ERP software using PHP 4 (no framework). Currently, it works fine from the business point of view except for some bugs here and there. Presently, about 4-5 people use it. The company's plan is to offer it as a product to clients with some modifications.
The code is messy. Its partly also because 5-6 devs have worked separately on it in the last 15 years.
I am the only person on the tech team now and the chances of adding more people are negligible.
Should I recommend management to upgrade to PHP 7.1 and a framework ?
The thing is that building the whole thing from scratch can take around a year since I am alone here.
I repeat the business needs are being met to a great extent as of now.
Answering questions by jonrsharpe:
Currently our executives use this ERP. We are not selling this software now but the vision is to do that in future. I agree with you when you say "Given the size of the company it seems unlikely they could keep doing whatever it is and develop, sell and support a large piece of software". The major issue is that the management wants to see outputs that improve their day-to-day business (which relies on this ERP) . Their bias for action prioritises short term goals over long term ones. When I was hired, I was told that there is a working piece piece of software with a few bugs here and there. They wanted me to test them and fix them (now these bugs are really minor ones as far as the functionality is concerned). So, I am looking for a solid reason to first convince myself to upgrade. The old dev had left before I had joined and the management has little tech knowledge.