If the phone memory is getting full, first check for and remove things you no longer need:
Instead of removing, you can also move the files to the memory card.
The quality of your memory card may affect the performance of your phone greatly. To get the best out of your phone, use a fast 4–128GB card by a well-known manufacturer.
Use only compatible memory cards approved for use with this device. Incompatible cards may damage the card and the device and corrupt data stored on the card.
You can copy photos, videos, and other content created by you between your phone and computer to show or store them.
Make sure you put the files in the right folders on your phone, or you may not be able to see them.