Assuming the generic Android settings model here;
a bit of pre-setup
On the phone:
Open your phones ettings.
Wireless and networks
select 'Mobile Networks' (Should be at the botton)
Make sure 'Data Enabled' or 'Enable Packet Data' is enabled (This should be the top option)
and that 'Use only 2g networks ' is UNticked. (if this option is there)
go back one menu level.
select 'Tethering & Portable hotspot'
select 'Portable Wi-Fi Hotspot' to enable it.
select 'Portable Wi-Fi hotspot settings to setup connection encryption (I believe it has the option of WPA-PSK)
set a password for the connection (so others cant just hijack your mobile data)
You should get an extra icon on your notification bar to show the Wi-Fi Hotspot is enabled.
Also make sure the phone is fairly close to the PS3 - 4-6 meters is about the furthest I'd want to go.
On the PS3
Second to the far left of the XMB to get settings.
Network settings
Set up connection
Wireless connection
The default name AndroidAP (Or if you changed it it will be that name for your connection) will show up
Select it and use the PS3 onscreen keyboard to type in the security key when prompted
When selecting a setup method 'easy' will suffice as the phone provides it's own DHCP settings.
run the internet test and assuming you have data available on your account and have cellphone coverage it should pass! and allow you to update the ps3/sign in
and play online.
Sorry if any steps are out of place/order this is all just off the top of my head.
Kurtis