I appreciate you reaching out in the Community. It's important you're able to access time-tracking on your iPhone so you can easily track and bill customers for the number of hours consumed in a project or activity.
QuickBooks offers this feature which allows you to save tonnes of time and at this time, you'll have to use it on the desktop app or your web-browser. It's also important to note that you can use this feature only with QuickBooks Online Essentials and a Plus account only. Here's an article with more info: How to turn on and set up time tracking.
Give this a try and if you have questions, I recommend reaching out to our support team using this link here.
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