Guide
Reduce video size on iPhone to free storage
Shrinking videos can free space on your iPhone. Final size depends on the source. Compression runs on-device.
4K and long clips take gigabytes. Re-encoding at a smaller preset can reduce the file you keep or send.
Video & Photo Compressor shows the measured size after encoding so you can decide whether to save. If you still need the original, keep it in Photos or Files.