Hi, here's how I solved it on my iPhone 8 with iOS 11.2.1 (when I purchased the phone it came with iOS 11 and I updated it immediately after setup to 11.2.1). When I enabled call announcement I was surprised to hear a male voice (under iOS 10 I had Siri female), so I digged into this, and found the solution: go to Settings / Siri and Search, then turn on Press Home for Siri (of not enabled yet - in my case it wasn't because when setting up the phone I prefer to do most of the final setup later, so during the initial setup I just skipped the Siri part). Then you'll be given the options to choose from various voices for Siri. I guess you'll see that in your case you have English (United Kingdom) Male, so just change it to English (United States) American Female and you are safe to turn off Press Home for Siri (should you wish to). Solved the issue immediately (asked my wife to call me and enjoyed my female voice back again). Hope this helps!