Safari web page

[che...@momentumglobal.co.uk]

I found on my son's phone a google web page open with 'pornographic material' written in the search box. Underneath the search box we're several pornographic images. My son said he has never opened that page. His web history for that day has the 'search material' listed around 10 times which I presume is because he has opened a number if the images? Could this in anyway be spam? The thing that worries me is the search was specific, though slightly misspelt and why would his history state this too? Can something other than my son type in a google search on his phone- is a spam thing capable if this?
iPhone 4