Existing Wording
If capturing a phone, fax or similar contact point, the value should be a properly formatted telephone number according to ITU-T E.123. However, this is frequently not possible due to legacy data and/or recording methods.

Comments
I believe that it would be better to use the URI format from IETF RFC 3966 (no spaces).

From RFC 3966:
However, even though ITU-T E.123 [E.123] recommends the use of space
characters as visual separators in printed telephone numbers, "tel"
URIs MUST NOT use spaces in visual separators to avoid excessive escaping.

Grahame's Comments
no. many implementers cannot conform to this in CDA - and it's about more than just spaces. And it brings no value to end users, to strip comments out. This can be applied as a rule in a profile if desired