What is actually learned in classical conditioning? The answer varies depending

According to Pavlov, what is learned is an association between two stimuli, the unconditioned stimulus and the conditioned stimulus.
Contemporary psychologists think that what is actually learned is information conveyed by one stimulus about another.  For example, if A occurs then B is likely to follow.
Rescorla demonstrated that pairing of an unconditioned stimulus and a neutral stimulus is not enough to produce learning. 
To become a conditioned stimulus, the neutral stimulus must reliably signal, or predict, the unconditioned stimulus.
For example, if food occurs just as often without a preceding tone  with it, the tone is unlikely to become a conditioned stimulus.
For example, a person working in an office may be allowed to receive outside phone calls only in emergencies.  If that person receives three emergency calls in one day, and no other calls, he or she might develop a conditioned response of anxiety to the ringing of the phone.
But if the three emergency calls occurred randomly among 50 routine business calls, a conditioned response probably would not develop.