Second: Doing a full rewrite with a junior team is not going to end well. They’ll just make other mistakes in the rewritten app, and then you’ll be back where your started.
You need to gradually introduce better engineering practices, while at the same time keeping the project up and running (i.e. meeting business needs). I’d start with introducing revision control (git), then some static testing (phpstan, eslint), then some CI to run the test automatically, then unit/integration tests (phpunit), etc. These things should be introduced one at a time and over a timespan of months probably.
I’d also have a sort of long term technical vision to strive against, like “we are going to move away from our home-written framework towards Laravel”, or “we are moving towards building the client with React Native”, or whatever you think is a good end outcome.
You also need to shield the team from upper management and let them just focus on the engineering stuff. This means you need to understand the business side, and advocate for your team and product in the rest of the organization.
You have a lot of work ahead of you. Be communicative and strive towards letting people and business grow. I can see you focus a lot on the technical aspects. Try to not let that consume too much of your attention, but try to shift towards business and people instead.