All I see is a dead crowd and people on their phones
All I see are a dead crowd and people on their phones
Which one is grammatically correct?
In the sentence, ""All I see" is the subject.
All I see is blue.
All I see are blue.
Something is blue.
Something are blue.
Therefore, what follows after the verb is not important in deciding the form of the verb (singular or plural).
Considering that "All I see" functions as a singular (even if it might be composed of several parts), the verb must also be singular.
Modern spoken English has a lot of blur about number, and we go from a singular noun for something (crowd) to a plural (people) often without noticing. Both read perfectly well but have slightly different shades of meaning.
Assuming a speaker such as a person entering a bar ... If the crowd is metaphorically dead because it is comprised of people on their phones, is reads perfectly fine: "and people on their phones" is explanation.
Assuming a speaker such as a policeman approaching some horrible crime scene and the crowd is literally dead and other people are on their phones, are stresses the plurality across the and: there are dead people and there are also people on their phones.