Here is the sentence:
Local fixed line calls were the highest throughout the period, rising from 72 billion minutes in 1995 to just under 90 billion in 1998.
I think there should be the phrase 'the number of' before the subject 'local fixed line calls' because the following predicate said something was the highest. I'm not sure whether this case is a grammatical omission. If so, is it customary to omit phrases like 'the number of' and 'the amount of' when somebody describes the quantity of something?