What are you interested in building? I sure wouldn't be learning to build native mobile apps if I didn't want to work on them ;) Basically you should learn things that grow your career in the direction you want it to grow. Are you wanting to be a frontend, backend, full stack, mobile specialist or something else? If you want to stay in the backend realm I would recommend you learn something other than PHP as it does seem to be declining.
MEAN is not bad, although I would be thinking twice about Angular with the 1/2 split; if you're going from scratch I'd probably go MERN over MEAN right now. But even then, it depends a lot on your circumstances - do you have a lot of MEAN/MERN devs around that can help you if you get stuck? Is one of these options the chosen stack where you work? All questions that might guide you to an answer.