Should I inform my bosses that I'm about to start doing a PhD research?
Of course you should!


Certain duties such as a committee meeting would require you to ask for a leave permission from your company. If you break it then, you'd be in trouble. In certain institutions, it is mandatory to provide an NoC (no objection certificate) from your company as part of the PhD admission process. You should've done it before, but the earlier you inform him, the better.