No direct evidence. Only circumstantial evidence. As your friend was the only person sitting beside you at time of incidence, it is probable that only he could have stolen your phone as no one else was around at time of occurence.
If you want to, please file an FIR u/ Section 154 crpc against your friend. The FIR would look something like the attachment, along with the charges below:
Personal details: Name/address/contact no etc
Place of occurance: Where did incident take place?
Dt.& Hour of occurence: which date and at what time incident took place?
Offense complained of: In your case it would be theft (include property particulars)
Describe your friend/whoever you suspect of having stolen your phone.
Sign it with your name and signature on the dotted lines. And include a concise statement of facts on why you want to lodge the FIR against your friend.
Make 2 copies of FIR. One for yourself. One for/at police station.\