To find out which iPhone model you have, go to Settings > General > About. To the right of Model, you'll see the model number.
iPhone XS Max: A1920, A2097, A2098, A2100.
iPhone XS: A1921, A2101, A2102, A2104.
iPhone XR: A1984, A2105, A2106, A2108.
iPhone X: A1865, A1901, A1902.
iPhone 8 Plus: A1864, A1897, A1898.
iPhone 8: A1863, A1905, A1906.
iPhone 7 Plus: A1661, A1784, A1785.
iPhone 7: A1660, A1778, A1779.
iPhone SE: A1723, A1662, A1724.
iPhone 6s Plus: A1723, A1662, A1724.
iPhone 6s: A1633, A1688, A1700.
iPhone 6 Plus: A1522, A1524, A1593.
iPhone 6: A1549, A1586, A1589.
iPhone 5s: A1453, A1457, A1518, A1528, A1530, A1533.
iPhone 5c: A1456, A1507, A1516, A1529, A1532.
iPhone 5: A1428, A1429, A1442.
iPhone 4s: A1431, A1387.
iPhone 4: A1349, A1332.
iPhone 3GS: A1325, A1303.
iPhone 3G: A1324, A1241.
iPhone: A1203.