Thanks for the correction. It makes sense to me that it was a pay phone. That would eliminate some of the issues that would be likely with a free one.
I can imagine the owners/landlord wouldn't want the renters to be able to make free calls all day. Not worry about paying for them.
Marina said that Oswald was worried that the landlady would find out that he had lived in the USSR. And that the FBI might find out where he lived. So it's understandable that he would switch to English to try and hide that fact.
From "Marina and Lee". This is after Marina asked Ruth to phone the rooming house so she could talk to Oswald. Ruth did but when she asked to talk to a Lee Oswald she was told no one by that name lived there. Oswald would be oddly (to me) furious with Marina over the call. He thought it would get him "into trouble."
Here's the account:
"The next day, Monday, November 18, Lee called as usual at lunchtime. "We phoned you last evening", Marina said, "Where were you?"
"I was at home watching TV. Nobody called me to the phone. What name did she ask for me by?"
Marina told him. There was a long silence at the other end. "Oh, damn. I don't live there under my real name."
"Why not? Marina asked.
Lee said he did not want his landlady to know he had lived in Russia.
"It's none of her business," Marina retorted.
"You don't understand a thing," Lee said. "I don't want the FBI to know where I live, either....You and your long tongue," he said; "they always get us into trouble."