I really really love Sonic Alert Products
If you call or email Sonic Alert directly, I've very sure they'd be happy to help you out!
Sonic Alert has a number of fantastic alarmclocks - many of which are also receivers for other devices (phone, doorbell, etc)
Which phone are you trying to "hear" - a land line that plugs into the wall or a cell phone ?
If you are looking for a land-line phone signaller then the perfect option might be the
Alarm Clock and Telephone Signaller
with Super Shaker™ - SBT425ss which is available through a Sonic Alert distributer or directly from Sonic Alert themselves !!
I can't say enough good things about Sonic Alert ... I've had my "system" from them (phone - with room light on/off, doorbell,sound signaller, remote flasher & Sonic Boom Alarm Clock) for many many years (10ish ?) and they still work perfectly !!
I LOVE them and they're very easy to "install" (plug into wall), use, move around etc - and it's easy to add components that will "communicate" with the existing system.
For cell phone - I use a sound-signaller set to sensitive which I place right next to the cell phone ... when the cell rings, the sound signaller sends the signaller to my "receivers" ... it works very well - but I find that you need to select a "Traditional phone ring" ringtone for it to work the best.