Keeping a spare smartphone around the house can be a wise move. When a family member loses their phone, you have a decent alternative ready, because no one wants to use your five-year-old Galaxy. You also don't have to rush to buy an expensive replacement, but can wait for a good deal to present itself. The Moto X4 makes an excellent spare phone, and at just $130 ($10 below the $140 it had previously dropped to), it won't cost you too much.
This price is for the Prime Exclusive 32GB variant of the Moto X4, which comes with Alexa and a bootloader that can't be unlocked, though this shouldn't be a problem for most, as the phone is bloat-free and runs Android 9.0 Pie. The mid-range Snapdragon 630 SoC isn't the newest around, but it'll suffice for everyday use. The pocketable 5.2-inch screen size, IP68 water resistance, and the headphone jack are additional bonuses. You can check out Ryan's review of the phone, but keep in mind that a lot of the criticisms pertain to the $400 launch price.
Amazon has other Prime Exclusive phones on sale too, like the Moto G6 for $180, and the LG K30 for $140. I think the Moto X4 is still the better deal, though the Moto G6 is worth considering if you prefer a larger screen.