They can be used a singular or plural noun, and I think that can influence the verb choice.
We sometimes use "they" as a singular noun when we don't know or don't to include the gender.
They lost their phones. - Plural subject noun is being used, so Multiple people each lost multiple phones.
They lost their phone. - Singular subject noun is being used, so one person (could be male or female) lost his or her phone.
They lost their phone - could imply a plural subject (maybe a married couple who share a phone) lost one phone.