Is the swimming pool responsible for losing your mobile phone?

If the locker you use at the swimming pool is self-service, then the legal relationship between you and the swimming pool is only a loan contract. If the items are lost during the loan contract, the swimming pool will not be responsible for compensation. But if you store it manually, then there is a legal custody contract between you and the swimming pool. The swimming pool should assign a dedicated person to be responsible for the safety of your stored items. In addition, according to the provisions of my country's "Contract Law": if the custodian damages or loses the custodian, he shall be liable for damages.

Furthermore, the four conditions that must be met to constitute damages are: fact of damage, illegal behavior, causal relationship and subjective fault. You said that your mobile phone was stolen, but the cabinet was not broken into. One of the reasons may be that in many swimming pools, one key can open multiple storage boxes. If your phone is stolen because of this, this is a typical subjective fault of the custodian in the custody contract. The swimming pool should compensate you for your losses.