All 314-935 numbers belong to Washington University in St. Louis.  I went there, and I also get a lot of calls from this number.  I would agree with LocL, that this probably is one of the numbers they use for fundraising.  I prefer not to get these calls because I already respond to a number of the direct mail campaigns, and the callers always manage to "guilt" me into giving more.... so I don't answer.

I have no idea who this is, but they call every night around 7 PM from this number or 314-935-8019 and no message is left. When I try and call back it just rings endlessly

Wash u med school, asking for donations.