someone's YouTube comment: KGB tapped her phone

I was truly moved by Benny and the gang's attempt to help Beth in Russia, so it never occurred to me at the time, but it makes sense

Borgov surprised her after the adjournment because the KGB had her phone line tapped. Everything Benny, Henry and the boys told Beth would've been passed along to Borgov, who proceeded to take a different tack.

Guess it doesn't matter too much to the plot - the point of that whole final sequence is to show Beth, even without (or especially without) booze and pills, she has plenty of people in her corner, including Borgov himself.