Why would the ISBLANK not validate if I use t...

[Henry_Scott]

Why would the ISBLANK not validate if I use this in a Error_Message_If_Invalid for a Phone Number? It allows the field to be empty The other parts of the formula of CONTAINS and the LEN of TEXT does validate

=IF(OR(CONTAINS([_THIS], " "), LEN(TEXT([_THIS])) <> 10, ISBLANK([_THIS])), “No Spaces, Phone Number Length should be = 10, EXAMPLE 0821234567 OR 0125556666”, “” )