Why didn’t they just stick to the airplane phones

Because people make mistakes and some boomer at the CIA assumed that cell phones would work. :shrug-outta-hecks: I suppose it also makes it more likely that their relatives would recognize the number and pick up the phone.

People say "do you think it would be possible for them to pull off such an elaborate plan without making any mistakes?" And when you point out an error different people say "do you really think they would make such a big mistake?"