Cellphones, Providers, and Plans → when others are on their phone.........

When others are talking on their cell phones does that slow down the speed of the internet on my smartphone? How much bandwidth does one person use when talking?

the answer is yes and no. if a large numebr of people are all using the resources of the same tower then it may slow your speeds. the resources give priority to voice calls, and each tower only has so much bandwidth. BUT in nearly all cases there is enough reserved that you won't see a decrease in DL speeds.

also keep in mind that your speed drops drastically as you get into weaker signal areas.