Frequency Incompaitiblity?

I have a Linksys WRT54GSV2 wireless router which is 2.4GHz. I have it
set to Wireless Channel 11 which is 2.462GHz. I have always had
conneciton problems in a pretty close location around my fathers
computers in his office. I just realized his office phone says
"2.4GHz" as a major feature. This would be good except I remember
reading that there will be interference or something. Is this what is
causing the connection errors? Is there any way I can fix this without
buying new stuff? (I am pretty sure he NEEDS that phone). I guess if
the only alternative is a new router, what is one that will give same
features, speed, and performance but on a different frequency than the
phone? Thanks!

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