iPhone Text messages hacked?

Today I was called into employee relations. Someone who left the company is trying to destroy my reputation and is outright not telling any sort of truth. It hurts, but I know the truth. To remind myself I am not crazy I wanted to review the text messages that the person sent me a few months to years back- which clearly demonstrate that persons maliciousness- but I discovered they are all gone except the last few messages. Has my iPhone been hacked? I would never have deleted them because I knew what this person may be capable of… luckily I screenshot some of the texts a few weeks back- but now where did all the others go? Is there anyway to recover what has been deleted? Why is it only this persons texts? Was it possible I was hacked to remove any sort of evidence?