I have set my micro sd card as internal memory before, but now, my phone is not working. However my phone started functioning normally when i tried removing the sd card. How can I fix my sd card back as portable storage if my phone doesn't even work every time I insert the sd card on it?
If the card was set as "Internal" storage then it would have been encoded. Because of this no other device would be able to read it and the original device, if say reset, would no longer be able to read it as well. This could be a cause of the issue.
If not, and the phone wasn't reset, then I would look at either the card being damaged, or the port is damaged.
To test it, first try restarting your phone (power it off and then back on). It may well allow the card then. If it doesn't, try a different card. If the phone allows that new card to work, then the old card is the problem and would need replacing. However, if the new card won't work either, then the port may well be damaged.
If the port turns out to be the problem, and if the phone is under warranty, I would suggest contacting the manufacturer. If it isn't under warranty, then try a local tech.