Be concerned.
Something is not right. Likely an electrical short....
Immediately power down, unplug and replace the cables with the standard power cables that came with your PSU.
Inspect everywhere for signs of damage: melting, discoloration, swollen components. etc. before reinstalling the replacement cables.
Hopefully the heat problem will go away if the problem is indeed cable related.
If not:
Update your post to include full system hardware specs and OS information.
Include PSU: make, model, wattage, age, condition.
Where did you buy the Phanteks cables?