Well if your phone is running any Android below "Marshmallow" that isn't possible. They require at least "Marshmallow" to set the SD card as "Internal" storage rather than the standard "External" storage.
If you are running, or can upgrade to, "Marshmallow" then you have a shot. It will then depend on your phone's manufacturer. Some have limited the ability, even when running the right OS.
NOTE: You will have to start with a blank SD card though. The reason for this is that the card will be formatted and encoded when it is converted to "Internal" storage, erasing anything that was already on it, and making the data unreadable by any other device (directly from the card).
If you can do the upgrade, or are already running...