^start of string
Group 1(\+44\s?7\d{3}|\(?07\d{3}\)|\(?02\d{2}\)?|\(?01\d{3}\)?) 1st Alternative\+44\s?7\d{3} \+the literal + (4310 / 538 / 2B16)
\s?optionally matches any whitespace character
7the literal 7 (5510 / 678 / 3716)
\d{3}a digit, repeated exactly 3 times
2nd Alternative\(?07\d{3}\) \(?optionally matches the literal ( (4010 / 508 / 2816)
\d{3}a digit, repeated exactly 3 times
\)the literal ) (4110 / 518 / 2916)
3rd Alternative\(?02\d{2}\)? \(?optionally matches the literal ( (4010 / 508 / 2816)
\d{2}a digit, repeated exactly 2 times
\)?optionally matches the literal ) (4110 / 518 / 2916)
4th Alternative\(?01\d{3}\)? \(?optionally matches the literal ( (4010 / 508 / 2816)
\d{3}a digit, repeated exactly 3 times
\)?optionally matches the literal ) (4110 / 518 / 2916)
\s?optionally matches any whitespace character
\d{3}a digit, repeated exactly 3 times
-the literal - (4510 / 558 / 2D16)
\s?optionally matches any whitespace character
\d{4}a digit, repeated exactly 4 times
$end of string, or before its final line terminator