It is going to depend on which OS your phone is using. I believe Marshmallow is being used in the G5. This is the only system (Marshmallow) that allows for making a SD card internal rather than external. However, I believe that LG has added it's own restrictions to the phones though, preventing some from allowing the change. If there is a way around the restriction they put, I do not know of it. You would have to ask LG about it.
That is the only way to move apps to the card, and also have some download direct to it.
You should check with them first, to see if there is a way around it. If there is.... Then you can change it to internal, but still not all files and apps will go there. Some sites, as well as some apps, still don't...