"Works with iPhone" can mean three very different things. Here's what each route involves day to day, and which printers in our catalog document which route.
The three routes
Route
What it looks like
Printers that document it
AirPrint / Wi-Fi network
Open the label PDF, tap Share → Print, choose the printer. No extra app.
Rollo Wireless (AirPrint certified per Rollo), Brother QL-1110NWB and QL-820NWB (Brother references AirPrint)
Bluetooth + maker's app
Save or share the PDF into the maker's app, confirm the size, print.
Printer plugged into your router; the phone prints over the network.
Arkscan 2054A-LAN (Arkscan lists iOS for the LAN model only)
Bluetooth is not AirPrint. A Bluetooth label printer usually won't appear in the iPhone's standard print dialog; you print through the maker's app. That works, but it depends on the app accepting the label format your shipping platform produces.
USB-only printers can't be used directly from an iPhone or iPad. Rollo, for example, says its USB model doesn't support phones or tablets.
Android
Android support varies more by method. MUNBYN and Phomemo route Android through their apps; Brother uses iPrint&Label; Rollo lists Android for its Wi-Fi printer without detailing the method; Brother documents Android printing with the USB-only QL-1100 through a USB On-The-Go cable. Check the specific review for the condition.
A reliable phone workflow
Buy the label in your shipping platform and choose the 4 × 6 in label format if offered.
Open the PDF (not a screenshot of it).
Print through AirPrint or the maker's app.
Check the paper size is 4 × 6 and scaling is 100% / actual size, so barcodes aren't shrunk.
Print one test label on a new roll or stack before a batch.