I've Been to Your Future.

On the eve of college graduation, Ye Fan finally plucked up the courage to confess to Tao Tao, whom he had been secretly in love with for many years. However, Tao Tao died in an accidental car accident, and the two were separated from each other. While packing up Tao Tao's belongings, Ye Fan accidentally obtained her old mobile phone and gained the ability to connect to the past. In order to save Tao Tao, Ye Fan decided to launch a time and space rescue.