This might be a stupid question but can I take the SHSH blob from someone else's phone that has os 3.1.3 and somehow use it to jailbreak my phone. Thanks

I think you will find that they are unique, that's why it is recommended to do a backup before firmware updates

They are defo unique, u cannot use another phone shsh.

U needed to save using the option in the cydia app

Syscon and Mattybaby19 are 100% correct. SHSH files are unique per device and cannot be hacked, faked, cheated, stolen, etc. If you didn't get them from Apple for your device for the revision of firmware you need them for while Apple was signing, you're out of luck.