If you have more than one network in the restaurant (e.g. a customer network and a staff network)...
Make sure the iPad and the test phone are on the same network.
If this fixes your problem, you can stop reading this page now (as it gets a bit technical).
Some professional grade networks are configured to block peer to peer traffic (also sometimes called Client Isolation or Wireless Client Isolation).
Which means that the bonjour advertisements from the Pocket Waiter iPad don't ever reach any of the phones on the network.
If you operate your own network, you can reconfigure it to allow peer to peer traffic (also sometimes called disabling client isolation).
This is free, costs you nothing, but can sometimes take a little time to find the network admininstrator (or in some cases, the network admin password).
If you can't do option 1...
You can also go into the Pocket Waiter settings screen on the Pocket Waiter iPad and enable Allow Gateway Connections.
It allows your customers' phones to communicate with your Pocket Waiter iPad via the the pocket waiter website.
This is a classified as a premium feature in Pocket Waiter.
If you feel you have to go with option 2, you'll probably also need to get a Bluetooth printer as the Pocket Waiter iPad will probably also be blocked from communicating with printers on your WiFi.