If you're on a text only browser then you don't get much choice about the width...
Don's Home > Web Developement > Mobile Friendly > 320 x 480 Image
 
Width is confusing. iPhone retina display, crams two device pixels into each CSS pixel on the screen so the CSS or display size is half the "reslution"
See: mydevice.io know your mobile device (pixel-ratio, CSS width, features) 
Some early device display sizes
          Device (CSS) size
iPhone 3,4              320 x 480
iPhone 5                320 x 568
iPhone 6,7,8            375 x 667
Samsung Galaxy S, S2,   320 x 533
Samsung Galaxy S3 - S7  360 x 640

1920 x 1000

last updated 4 Mar 2018