Niet-telefoongerelateerde tekens verwijderen:
var phone = "er+f375g25123435s67";
phone = phone.replace(/[^+|\d]/g, ""); //result = "+3752512343567"
Vervolgens om het telefoonpatroon te matchen:
if (phone.match(/^[+][0-9]{12}$/))//or /^[+][0-9]{13}$/ for 13 digits
...
EDIT: Here's what I was able to come up with for the test & replace:
phone = $(this).val().replace(/^[^+]{1}/, '');
if (phone.length > 1)
phone = phone.substring(0,1) + phone.substring(1).replace(/[^\d]/g, '');
if (phone.match(/^[+][\d]{12}$/))
phone = phone.substring(0,4) + " " + phone.substring(4,6) + " " + phone.substring(6,14);
Located here: http://jsfiddle.net/cabbott/KaYeJ/