They spy on calls to Russia?
They do, but I think electronic eavesdropping involving U.S citizens or officials is not legally kosher past 30 seconds within the U.S. unless you get a FISA court warrant. But at present things like laws are all but quaint and out-of-date and annoying and not followed by the government. I would say it is certain Flynn chose every word carefully and as former head of DIA knew the conversation was being monitored. Deep State is seriously threatened by Flynn and have sought to take him out by any means necessary. Scary f-ing times we're living in.
NSA has recorded every electronic emission worldwide since the early 1960s. Not a secret. Russian intercepts have been and remain a priority. Not a secret.
If you want to know more there are one or more books published by ex-NSA staffers.
FYI: All the Eddy Snowjob released to the public was also not a secret. What he stole was; what he gave the Russians and Chinese was.