Many of the phones come with memory card slots that work with a spring loaded mechanism. You have to push in the memory card inside the slot and it gets locked in. When you want to take it out, you have to push it again and the spring inside the slot throws it out. The popular Apple iPhone has a memory slot like this. But over a long time of usage, the spring may get corroded and can stop working. So now when you want to take the memory card out, the spring does not work and the card gets jammed inside the slot forever.
The only solution for the jammed micro SD card in this case would be to take the phone to a technician or repair shop. There they would open the phone up and take out the card from the memory slot. But you can prevent all this by using a small piece of adhesive tape.
All you have to do is use a small piece of adhesive tape (1 cm x 3 cm) and fix it on your micro-SD memory card. Almost 1 cm gets stuck on the memory card and rest 2 cm is folded up so that it keeps hanging without getting stuck on anything.
Now you can insert this card inside the memory card slot like usual and then push the hanging part of the adhesive tape inside too. Later when you need to take out the memory card, you can try pushing it and if the spring mechanism fails, you can just pull out the adhesive tape. Along with the tape, the memory card will also come out.
You can use any type of adhesive tape for this, but a good quality tape is recommended. The phone gets heated up during the everyday usage as well as when you recharge the phone battery. So if you use a low quality adhesive tape, it will become loose and may not work when you would try to pull out the memory card.