If you install a tweak on a jailbroken iPhone and it causes problems. Sometimes it'll automatically reboot in safe mode to let you know there's a problem with the latest installed tweak.
But not always. So if you run into this problem and want to get into safe mode to remove the recently installed tweak that's causing problems. Here's what you can try.
Do a forced reboot by holding down the power and home button. Keep them held down until it shuts off then comes back on and you see the apple icon appear.
Once the apple icon appears on the screen let go of the power and home button then hold down the volume up button. Keep it held down until the iPhone reboots and you see the slide to unlock screen.
It could take a couple of minutes for it to load. Be patient. One time it took me almost 3 minutes. But just keep holding that volume up button down until it loads.
You'll now be in a sort of safe mode. That means all the tweaks you've installed that run in the background will not be running. The icons will change order and leave their folders. Don't panic.
Now you can go into Cydia and remove the tweak that's causing you problems. When you're done give your device another force reboot to bring everything back to normal.
I hope this is helpful to someone.