This is question 1.22 from the textbook:
The Gallup Poll uses a procedure called random digit dialing, which creates phone numbers based on a list of all area codes in America in conjunction with the associated number of residential households in each area code. Give a possible reason the Gallup Poll chooses to use random digit dialing instead of picking phone numbers from the phone book.
It's more cost effective and saves time.
Since individuals have the option to remove their phone numbers from the phone book, pollsters using the phone book for their number base would, at least, encounter convenience sampling.
It sounds like by choosing to do random digit dialing, it would be easier to have a machine that works twice as fast do it.
It could help eliminate unconscious bias. Someone picking numbers from a phone book, even if they don't mean to, might consistently pick names towards the back, front, or middle of the phone book without realizing it. It also reduces the risk of conscious bias, because (a malicious) pollster can try to predict someone's potential responses by their name or location and skip over them/target them to skew the data.
It is most likely trying to use a stratified random sampling method where the area codes are the strata and the number of samples for each strata is determined by the number of households in each area. According to many introductory statistics videos, stratified sampling is one of the most effective sampling techniques.