i want to achieve below scenario in ms crm

i have below scenario to achieve

i have 5 fields in a form

1. name

2. email

3. phone

4. age

5. DOB

in 5 field i can able to edit only one field(phone) remaining 4 fields i dont have permission to edit 

if any body trying to edit  "Phone" field immediately i want to show alert box

please give me you valuable suggestions to achieve this .

thanks,