Why does my router had to be reset several times a day?

Several times a day our router ( linksys 2.4 GHz) will kick us off the net. We simply unplug and then plug the unit back in and everthing is fine. My questions are 1) is my unit out of date? and 2) can wifi from cell phones kick us off line? I ask question 2 because most of the time that we get kicked off line, our son is coming in from work and I guess his phone has auto wifi and I asume it looks for a signal and kicks us off. Is this possible? Thanks for your time.