Intercepting international communications between the US (there is no distinction between US citizens and US residents) and known terrorist organizations is a lot different than spying on American citizens.
How is it different? If any person on either end of the phone is an American citizen, this is spying on American citizens.
Actually, it is different. Spying, in the typical sense, pertains to tracking an inidividual, collecting data on that person, an using it for criminal prosecution later on. The intercepting of electronic communication is different, since they are not after the individual, but the information to prevent an attack. And since there are millions of international electronic communications daily, the time is spent on screening the data from suspected terrorists rather than individual US citizens (again, "citizens" are not the target). As the FISA review court said,
the definition of an agent of a foreign power, if it pertains to a U.S. person, is closely tied to criminal activity. The term includes any person who "knowingly engages in clandestine intelligence gathering activities . . . which activities involve or may involve a violation of the criminal statutes of the United States," or "knowingly engages in sabotage or international terrorism, or activites that are in preperation therefor." So the argument of spying on everyday citizens is bunk, since again, it is the electronic communications between the US and foreign nations by people with criminal intensions.