If the power button is broken/unresponsive then obviously using it to try to reboot the phone is pointless. I also have this same issue. I can’t find any info anywhere about fixing or replacing the power button, DIY.
Either try to get it fixed somewhere or see how much Motorola charges. Otherwise, get another phone (NOT a Motorola!). I had my phone less than 6 months when it crashed and the power button hasn’t worked since. Motorola only has a 6 month warranty for this phone - now I know why.