ANSWER
1. This is an example of coverage error, because the sampling frame you are using isn't reflecting
the entire target population are interest. Because, spanish speaking people have fewer
landline than non-spanish speaking people. Hence, true populations are not in the sampling
frame.
2. In the sampling, they did not account for the error - they just used single random sampling.
3. Increasing the sampling size does not solve the problem. If spanish speaking people are not in
the position of the landlines, calling more people does not solve the problem. It might be that
you would get more people, but you still face the same problem - because the sampling frame
does not reflect the entire population. They need to select, in addition, more spanish speaking
people, or use a different sampling frame or sampling technique.