Shell input a string of numbers to determine whether it is a mobile phone number

[[email protected] ~]# cat phone.sh 
#!/bin/bash
echo " Enter a string of numbers to determine whether it is a mobile phone number "
read -ep "" num
if [[  "$num" =~ ^[1][3|5|8|9][0-9]{
    9}$ ]];then
	echo " It's a cell phone number "
else	
	echo " Not a cell phone number "
fi
[[email protected] ~]# ./phone.sh 
 Enter a string of numbers to determine whether it is a mobile phone number 
135
 Not a cell phone number 
[[email protected] ~]# ./phone.sh 
 Enter a string of numbers to determine whether it is a mobile phone number 
13567877777
 It's a cell phone number 
[[email protected] ~]# ./phone.sh 
 Enter a string of numbers to determine whether it is a mobile phone number 
135555553566
 Not a cell phone number 
[[email protected] ~]# ./phone.sh 
 Enter a string of numbers to determine whether it is a mobile phone number 
13131314dsv13z.
 Not a cell phone number