Quitting to competitor over phone?

I’ve been managed out of a US BB and have lined up a competing offer with another BB. Given I have 3 months of garden leave, had organised a trip with ~1 week buffer for signing the new contract. Now I’ve been told that will arrive 2 days after Im supposed to depart. Would cost me about $500 to reschedule/delay. Does anyone have any experience resigning over the phone? Not really expecting any references from the old shop, and it is unusual (pandemic) times, but curious on thoughts on whether that would be a massive no-no (versus traditional approach of doing it in person).