The HP LaserJet Pro MFP M28w is listed as a supported printer in About AirPrint - Apple Support. It normally means that an additional app is not necessary for printing when a printer and an iPhone are connected to the same network (home Wi-Fi router). It must be the same subnet. The following article shows how to print in such a case: Use AirPrint to print from your iPhone or iPad - Apple Support
However, the status of the public/apartment Wi-Fi here is unknown to us. Details would help. We do not know exactly how it works, and whether it functions as a "normal" home Wi-Fi router or not. If not, you would be limited to use the apartment Wi-Fi for Internet access only, but not for local networking. If so, another solution for printing would be needed.
One way to solve this could possibly be through a separate "travel router". The travel router would establish a wireless (Internet) connection to the apartment Wi-Fi system (the Hotspot Mode in https://www.tp-link.com/us/home-networking/wifi-router/tl-wr902ac/ is merely one example). The local Wi-Fi network provided by the travel router can be used for the connection of both an iPhone and a printer. Local AirPrint printing ought to be possible that way.