Sorry for the issues.
First,you'll need to start an account:
https://account.oneplus.net/sign-up
Then,you will have access to all the options afforded to all owners,whether you made the purchase or not.
Click on
SUPPORT at the top-right of the page & you'll be presented with FAQ's regarding filing a warranty claim/support/service.
An item worth noting:
Expeditious processing of warranty issues/claims/etc.. isn't OnePlus' forte',a lot of patience & perhaps persistence is in order.
AFAICT the only means of communication is via e-mail & expect 3-10 business days before hearing from them,so,make every communication count,leave no details out & be persistent.
I've dealt w/them on two occasions w/two different handsets.
1st go-around was a software/firmware bug that was fixable by both desktop remote &/or doing it myself (the latter I got to before they found the fix,which originated in the wild,not from OnePlus)
2nd go-around is exactly what you're experiencing (Phantom/inaccurate touchscreen responses),which is likely hardware-related,a flawed manufacturing process,using glue instead of tape,& is affecting the digitizer.
This has been in progress since Dec3,14 & no closer to a resolution today than I was over 3 weeks ago.I still have my defective handset & my patience is beginning to wear.
I still believe that OnePlus will honor the warranty,but,I will think twice,or more,before doing business w/them again if they don't pick up the pace ASAP.
Good luck w/your warranty claim & please keep us posted on your progress & don't hesitate to ask more questions if need be.