Accessing old photos from previous iPhones on current iPhone

How were the old photos saved? Did you have them in iCloud? If so, you should be able to just sign into the Apple Account used with iCloud and turn on the option to sync photos in the iCloud settings in your phone.

If you did not have those photos synced with iCloud, then you'll have to restore them from a backup of those old phones or (more practical if this involves multiple old phones) copy them from those old phones to another cloud-based service such as Dropbox or, if those old phones support it, an external storage device and then copy them to your current phone.

Regards.

Where did you save them?

If they were synced to iCloud Photo Library, you need to turn on iCloud Photos on the new phone.

If they were not, were they backed up or stored somewhere else?

Did you restore the new phone from a backup of the old one or transfer the data directly?

Did you sync the old phones to iCloud, or did you copy the photos from the old phones to your computer? Or did you back up your old phones to iCloud or to your computer? If you didn’t do any of these things then the photos are gone forever.