(Navigate to system/app and check if you playstore is named as vending.apk or phonesky.apk then do the steps mentioned below according to the names respectively)
1. Place the Phonesky.apk anywhere in the sd card. 2. Navigate to system/app using a file manager and rename Phonesky.apk to Phonesky.apkbak (So u have a backup of current playstore). 3. Place the downloaded Phonesky.apk to system/app using a file explorer. 4. Change the permissions to rw-r--r-- or 644 and apply. 5. Reboot.