Reduce photo size iPhone

Before taking photo

Compress photos before taking them: You can set your iPhone to capture photos in High Efficiency mode, which uses the HEVC format to compress images while maintaining their quality. To do this, go to Settings > Camera > Formats, and select High Efficiency

After taking photo

You can't reduce photo size on iPhone through regular iPhone Photos app without cropping it. You can see the size of photo or reduce it using 1 of 2 ways:

1. Email photo to your self and when you click on Send in Gmail it offers you 4 different sizes for the picture. 

2. Install one of the free apps to chage picture size. Two most popular ones are

- Image size

- Compress Photos&Pictures