A phone damaged at the sea

I took a phone from the yeshiva’s gmach ("gmach" – free-loan service) and went with it to the beach at night. I placed the phone on the sand next to all my clothes, near the lifeguard’s hut. Suddenly a big wave came, which was not expected to reach the lifeguard’s hut, and it washed over all the clothes and the phone, which was damaged and stopped working.

Am I obligated to pay the yeshiva for the damaged phone, or since the wave was unexpected, and I also put my other belongings in the same place, am I considered an ones (a victim of unavoidable circumstances) and exempt from payment?
P.S. A few minutes before the incident I saw a wave that came quite close to the lifeguard’s hut, but it did not occur to me that a wave would come that would actually pass the lifeguard’s hut and reach close to the canopies.

Shalom u’vracha 

You are a borrower, and a borrower is liable even for damages caused by unavoidable circumstances (ones).

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