Real/physical iPhone 6 Plus resolution is 1920x1080 but in Xcode you make your interface for 2208x1242 resolution (736x414 points) and on device it is automatically scaled down to 1920x1080 pixels.
iPhone resolutions quick reference:
Device Points Log. Res. Sc. Real Res. PPI Ratio SizeiPhone 12 Pro Max, 13 Pro Max 926x428 2778x1284 3x 2778x1284 458 19.5:9 6.7"iPhone 12, 12 Pro, 13, 13 Pro 844x390 2532x1170 3x 2532x1170 460 19.5:9 6.1"iPhone 12 mini, 13 mini 812x375 2436x1125 3x 2340x1080 476 19.5:9 5.4"iPhone XS Max, 11 Pro Max 896x414 2688x1242 3x 2688x1242 458 19.5:9 6.5"iPhone XR, 11 896x414 1792x828 2x 1792x828 326 19.5:9 6.1"iPhone X, XS, 11 Pro 812x375 2436x1125 3x 2436x1125 458 19.5:9 5.8"iPhone 6+, 6S+, 7+, 8+ 736x414 2208x1242 3x 1920x1080 401 16:9 5.5"iPhone 6, 6S, 7, 8, SE2 667x375 1334x750 2x 1334x750 326 16:9 4.7"iPhone 5, 5S, 5C, SE1 568x320 1136x640 2x 1136x640 326 16:9 4.0"iPhone 4, 4S 480x320 960x640 2x 960x640 326 3:2 3.5"iPhone 3GS 480x320 480x320 1x 480x320 163 3:2 3.5"