You can also use a computer to drag and drop the photos. Here is a good link from apple:
https://support.apple.com/en-us/HT205063
"Photos and videos
To move photos and videos from your Android to your iOS device, use a computer with iTunes:
Connect your Android to your computer and find your photos and videos. On most devices, you can find these files in DCIM > Camera. On a Mac, install Android File Transfer, open it, then go to DCIM > Camera.
Choose the photos and videos that you want to move and drag them to a folder on your computer.
Disconnect your Android and connect your iPhone to your computer.
Open iTunes on your computer and sync your Photos to your iPhone. You can find your photos and videos on your iPhone in Photos > Albums.
For help moving your photos and videos, contact Apple Support."