how to transfer a file of photos to another iphone

As Old Toad suggests, AirDrop may be the best way to transfer pictures--they'll automatically end up as proper members of the Photos Library, although they won't necessarily carry all their attributes. They won't be in albums, for instance.

In order to not lose the album organization and other information, it may be that the only way would be to use iCloud. You could get enough iCloud storage for one month, and then connect both phones. The Photos Libraries would merge into identical libraries with all albums and folders intact. Photos would do its best to avoid duplicates. Then turn off iCloud and cancel the subscription.

By file do you mean Album in the Photos library? If so select them all and do an Air Drop to the other phone. The other phone will have to be nearby.

If the other phone is not nearby or not an iPhone you can select them all (up to about 10 MB in in total size) and text or email them to the other phone.