A bug in the code from page 45 to find phone number reference?

[ravivanpong]

In order to answer how often agents refer to phone numbers, which has the pattern xxx-xxx-xxxx in the USA, the code on the page 45 is

sum(grepl('[0-9]{3})|[0-9]{4}', text.df$text))/
nrow(text.df)

There is a ) after {3}. What is this closing bracket for? Without it, the relative frequency of a phone number being referenced is 0.1445171.

Thank you for your advice.