https://www.ifixit.com/Teardown/iPhone+5+Teardown/10525
Toolkits are pretty cheap and can be sourced from any online shop or even local handphone shops.
Sir amiryagot Do you want to fix it with your self.. disasemblying is not easy
try this with your own risk
https://www.youtube.com/watch?v=ui-Eup6VyFw
Its better to bring it in cellphone specialist its a hardware related problem....I have patient before same as your phone mic issue and i solve the problem following the guide from the image that i send it here before........