“doesn’t it”/“don’t they” with “every” as a determiner

Every cell phone does that, doesn’t it? or Every cell phone does that, don’t they?

"Every" is a distributive determiner as reflected in the fact that it selects a singular 'head', hence "Every student is here", not *"Every students are here".

"Cell phone" has singular "phone" as head, so singular tag "doesn't it?" is the one you want. Note that you can use a plural tag with "all": All the cell phones do that, don't they?.