Here is my method of creating such a flared end of that plastic tube. It should be noted that almost all plastics, with the noteable exception of PTFE tubing, will flare with heat carefully applied to the end of the tube.
It is important to not apply the flamed heat directly, but to waft the flame carefully at the head end of the tubing, and watch as the flare develops progressively, and without the end of the plastic tube completely melting and thus sealing the end of the tube. It is worthwhile, therefore, to practice this method a few times on some tubing samples so that you can perfect the technique before making the move to using that heat flared tube in the tying of your tube fly.
You will need a length of appropriate tubing, a tube vice or other suitable vice, but you can hold the tubing by hand. You then only need a standard gas cigarette lighter (the petrol lighters do not produce a sufficiently consistent flame), and a steady hand.
Starting with a 3mm (1/8") od Nylon tube, precut to 1" length and placed into the jaws of the vice...
Next, the lighter approaches the head end of the tube...
Now waft the flame gently over the end of the tube, watching for the earliest formation of a melting and flaring rim of the plastic...
The beginning of the flare is just detected...
The flare is now completed...
Profile view of the completed flare...
End view of the completed flare...
The tube is now ready to start tying your fly on.
