Apple - Increase text size on iOS Safari

New Answer: Base on this and this

1. Bookmark this page
2. Navigate to your bookmarks and edit the bookmark added in Step 1
3. Change the name to "Increase Text Size"
4. Replace the URL with the code labeled "Increase Text Size" below
5. Repeat steps 1-3, but change the name to "Decrease Text Size"
6. Repeat step 4 but with the code labeled "Decrease Text Size" below

Increase Text Size: javascript:var%20p=document.getElementsByTagName('*');for(i=0;i%3Cp.length;i++)%7Bif(p%5Bi%5D.style.fontSize)%7Bvar%20s=parseInt(p%5Bi%5D.style.fontSize.replace(%22px%22,%22%22));%7Delse%7Bvar%20s=12;%7Ds+=2;p%5Bi%5D.style.fontSize=s+%22px%22%7D

Decrease Text Size javascript:var%20p=document.getElementsByTagName('*');for(i=0;i%3Cp.length;i++)%7Bif(p%5Bi%5D.style.fontSize)%7Bvar%20s=parseInt(p%5Bi%5D.style.fontSize.replace(%22px%22,%22%22));%7Delse%7Bvar%20s=12;%7Ds-=2;p%5Bi%5D.style.fontSize=s+%22px%22%7D

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Old Answer:

From this article

Here’s how you can use Reader in Safari for iPhone or iPad to increase text size of web pages:

1. Open Safari and go to any webpage with a lot of text, like an article or news piece

2. From any Safari browser window in iOS, hit the “Reader” button in the URL link bar to enter into Reader View – the Reader button looks like a series of lines atop one another

3. Once in Reader Mode, tap on the “aA” icon in the corner of the screen

4. Now tap the larger “A” button on the right side of the popup menu to increase text size

5. Tap the “A” button repeatedly to dramatically increase the font size of web pages in Safari Reader mode

Although this does not change the text size, you can pinch and zoom.

Lastly, you can change the font size. Although this will not help with Safari it will increase text size in other apps.

At least in iOS 13, there's a Safari setting that allows you to change the zoom level for all websites.

This will increase the text size. Depending on how the website's layout is designed, it might also result in horizontal scrolling, but hopefully these days a majority of websites are designed to avoid that.

To try this:

1. Go to Settings - Safari
2. Scroll down to "Settings for websites"
3. Tap on "Page Zoom"
4. Set whatever zoom level you want

Sadly, I'm not aware of any way to do this for individual websites on iOS. (Safari on Mac will remember the zoom level for specific websites, and let you set it in Settings - Websites - Page Zoom.)