Your phone is rooted right...!
And also you need to install recovery separately.. It will not come pre-installed you know that too right (just asking)
So now all you need to do is reboot your device and when it is on the Sony logo just start pressing vol down key and recovery will be opened...!
Sent from my ST25i using xda app-developers app
IF I HELPED YOU PRESS THANKS BUTTON
[DEVICE] SONY XPERIA U
[Model No.] ST25i
[Status] Rooted, BL Unlocked
[Android version] 4.0.4 (ICS)