If you are staying at a lodging in Roncesvalles, I would talk to either the hotel or albergue personnel to help get you a taxi. If you are arriving and being dropped off in Roncesvalles then need a taxi to complete the trip to SJPdP, then you can use Rome2rio, or google a taxi service from Pamplona or maybe Zubiri to meet you in Roncesvalles
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Most likely, you would need to take a bus, though, as there are no local taxis.