Look in your Moto G Play's Settings >> Storage menu and you'll see options to format a microSD card to be either Portable or Internal.
Just my opinion but you'll be much better off just leaving your card as Portable. If you do opt to change it to Internal, it's really important that you do so as an informed decision that this is a necessity, not just some idle experiment. This isn't something you should do out of curiosity, it's a commitment. The card's file system is changed in a major way, plus directly affecting the installed Android operating system on your phone.
It really isn't something you switch back and forth, use your card as either Portable or Internal. It's trivially easy to set the card as Internal, but more involved to reformat the card back to Portable. If you need more storage capacity for overall internal storage, you'll be better off just buying a phone with more internal storage. Set up a microSD card as Internal as a workaround, and be sure to research its pluses and minuses before rather than after.