pattern = /\A\d{3}-\d{4}-\d{4}\z/

pattern === '080-1234-5678'

pattern === 'Phone: 080-1234-5678'

pattern === '080-1234-5678 (mobile)'

lines = "1234\nabcd"

p(/\A\d+\z/ === lines)
/^\d+$/ === lines

p(/(B)\ to\ \1/ === 'B to B')

$1

/(?<number>[0-9]+)/ === 'abc-123'

Regexp.last_match[:number]

/(?<num>[0-9]+)[a-c\-]+\k<num>/ === '123-abc-123'

/(?<num>[0-9]+)[a-c\-]+\k<num>/ === '123-abc-123'

/(?<num>[0-9]+)(?<alp>[a-c\-]+)\k<num>/ === '123-abc-123'
Regexp.last_match.named_captures
# 2.4で来る

phone = '080-1234-5678'

p(/([0-9]+)-\g<1>-\g<1>/ === phone)

p(/([0-9]+)-\1-\1/ === phone)
/([0-9]+)-\1-\1/ === '080-080-080'

/(?<num>[0-9]+)-\g<num>-\g<num>/ === phone