Dropped Wireless Signal

I have 3 Macs connected wirelessly to an Airport Express. In the past few days the wireless signal to all 3 Macs has dropped twice. In other words, although there was a steady green light on the Airport Express, there was no signal indicated on any of the Macs. After power cycling the Airport Express & restarting the Macs, the signal was re-established.

Please excuse the lengthy explanation, but I am trying to see if I am on the right path to resolving this.

A tech at my broadband ISP confirmed that there was no problem with either the incoming internet line nor my cable modem. So the problem seems to likely reside downstream from the cable modem to the Airport Express.

I have a VOIP phone device connected between the cable modem & the Airport Express via ethernet cable. However, I have been advised by a knowledgeable person that even if the VOIP device was faulty, the Airport Express should nevertheless still transmit a wireless signal (of course there would be no internet connection). If this is true, it would suggest that the problem either stems from the Airport Express itself or possibly a new wireless network in my area operating on the same channel.

Does this reasoning make sense? Thank you for your patience & any help.

Take the VOIP device off and see if the problem continues. If no problem, but the VOIP device back on and see if the problem reoccurs. That should be instructive.

That idea occurred to me. But if the Airport Express always transmits a signal (regardless if the internet pathway is interrupted by a faulty VOIP device), that suggests that my computers should still be receiving a wireless signal --- which twice they have not. Maybe my reasoning is wrong here.

Also disconnecting the VOIP device will cut off my home phone service.