You can only pair one phone to the HomeKit, all other subsequent phones will share access to the iCloud Home via the invite process.
In the event that your phone cannot discover (find) Premis during the initial pairing process, try the following:
Delete any instances of your lock from your “Home”.
Press the “A” button in the upper left corner for ~10 seconds (the clearing process will be signaled with a beep). This will clear any previous pairings from the lock.
Restart the “Add Lock” process within the Premis App, and you should be able to “find” your lock and complete the pairing process.