Whenever my roommate turns on his laptop, the Wi-fi on my phone starts going in and out of connection to the network. It makes it to where wifi is pretty much unusable on my phone and I cant stand it so I have to switch to my mobile data; but i cant do this forever and I don't want to ask him. (Also, the wifi on my laptop works just fine while his laptop is on. Just my phone that is the problem. Nexus 6)
You can ask whoever set up the modem if there any priorities were set. Like this or that device takes priority over others, or if certain devices were given limitations. It would make sense if priority was given to devices owned by the WiFi owner, or for say computers over other devices.
When it comes to devices that lose connection more often than others, no there would not really be anything you could do to prevent that. If the ISP is losing connection more often, then your device may be one that just notices more.