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Doesn't work in contemporary iPhones. I had a nicer version of that from iSEMcon which was calibrated to the Apple input standard, but it got obsoleted when Apple (in their infinite wisdom) dropped their headphone/mike jacks and went over to Lightning.
The Dayton Audio mic requires a headphone jack, and the iPhone 10 does not have one. The best mic I'm aware of for the 10 is the Shure MV88, at about US$150, but it isn't a calibrated mic. I use the spectrum analyzer from Black Cat Systems on my XR just for field work, but if you want accurate spectrum analysis I recommend OmniMic II from Parts Express running on a PC.
For four dollars, this does a lot but you may not need the extras it offers. SPLnFFT. I have this and audio tools on my phone. For things like noise or spl measurements, setting up subs, and an fft screen, it's all I need. It is able to average spl over time which is useful to me but not to most audio guys. AudioTools has more capabilities but you have to pay more and each device you add is extra. A usb mic and a matching dongle for your phone should do the trick. You can use your phone's mic if all you care about are relative differences. If you need absolute accuracy rather than relative readings, you need a calibrated mic.There is an option for the one I linked to that comes calibrated.
The built in mic will not be useful below about 40Hz, maybe higher and I'm not sure AudioTools is accurate at 10Hz. You should check any apps you're looking at to see if they work there as well. They very well may not. Most audio devices don't do much good work below 20Hz, especially small diaphragm electrets.