In the case of a computer, even with the metal cases there are some serious harmonics radiating from the machine that could potentially interfere with the cordless phone.
That being said, all consumer electronic devices are Part 15 devices:
§ 15.5 General conditions of operation.(b) Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by industrial, scientific and medical (ISM) equipment, or by an incidental radiator.
In other words, consumer electronic gears is a magnet for interference.
In your case though I bet the problems you're having with a 2.4GHz phone have more to do with the more likely 802.11 gear, and somewhat less likely from wireless devices and controllers.
For example, my Pelican Spirit wireless game controller is absolutely worth crap around here. Too many wireless networks.