Especially if you encrypt your phone only with a PIN, it appears that it's quite easy to find that PIN. More than that, there is already a script on github which automates a lot of the process.
Now the unanswered issue is: Which command do you use to mount the partition in Linux?
In any case: be aware, the encryption does not protect you much at all. Of course that's what you should expect with a 4 key (usually numeric) PIN.