Hola Jeffrey Scott

These two sentences are using different subjects:

... donde no puedes hablar =  where you can't talk 

y no dejan usar el móvil = and they don't allow/permit to use the mobile phone (literal translation, so you can see it more clearly)

So, the second sentence is using the verb "dejar" which means "to allow" and it has a "they" as a subject, this they referring to a general they as in "people in charge/those who make the rules".

This is why you have two different subjects/conjugations there.

I hope this clarified it.

Saludos

Inma