Hello,
We don’t have iPhone 6, only newer versions of the iPhone, so we used BrowserStack to test with iPhone 6 and it does not display issues with the mobile menu https://gyazo.com/8fc5c15092d6f4495472ed6657862618
Do you have the issue with the menu with other versions of the iPhone? Did you try on other devices? Provide us with video of the issue for better understanding.
Regards