This seems to happen regularly.. for some reason, I suspect the wireless in the TC which is auto channel has picked a channel which is being used by bluetooth in the phone. The later ipad and later iphones can use 5ghz.. so that often gets them around the issue.
On a computer running airport utility.. go to the TC setup.
Go to the wireless area and setup wireless with SMB names.. ie short, no spaces pure alphanumeric.
Use a different name for 5ghz is also a good idea. Then you can force clients to join the 5ghz band. Don't worry if you cannot see it.
What is important is to lock the radio channel.. use 11, 6, 1 in that order.. to try.. ie if 11 works fine, then stick with it.
On v5 utility it looks like this.. you will need to tell me what you are using to configure the TC.
The pics above I have used WPA/WPA2 but it is better to use just WPA2 Personal for wireless security and use a password of 8-12 characters (more if you are paranoid type).. pure alphanumeric mix of upper and lower case plus numbers.
Tell us what uitlity you use to setup the TC.. if you use the iOS version someone else will have to help you.