Depends where you are, but it is debated. See for example this case: http://m.bbc.co.uk/news/uk-england-oxfordshire-23944993

http://www.bbc.com/news/uk-england-suffolk-19597446

http://news.bbc.co.uk/1/hi/magazine/4788910.stm

http://m.bbc.co.uk/news/uk-england-humber-22290619

Etc etc

Not to mention conversing with passengers.

It only takes a minute or two to eat, while a lot of people will spend the entire trip on the phone, either talking or texting.

Also, I don't know about you, but I don't have to think much about eating, compared to carrying on a conversation or reading.