First of All, Welcome to my BLOG On this Thread, you will find the Original link to Download Lenovo Phab Plus PB1-770M Stock ROM Firmware from Google Drive. Lenovo PB1-770M Firmware Package comes in a zip package, which contains Flash File and Flash Tool and Driver with How-to Flash Manual.
Device Name: Lenovo Phab Plus PB1-770M
Android Version: Lollipop 5.1
Install via: QcomDloader Tool
File Size: 2.3 GB
File Hosted: Google Drive
How to Flash Lenovo Phab Plus PB1-770M Stock Firmware
Step 1: Download & extract the Firmware on your computer.
Step 2: After extracting Firmware zip file you will find the Driver and Installation Instructions.
Step 3: Install Latest available USB Drivers (Just skip this Step if your Computer already have).
Step 4: Follow the instruction to flash the firmware your Lenovo smarthphone.
Download Lenovo Phab Plus PB1-770M Firmware Update