http://www.fccenvironment.co.uk/milton.html
"The waste that is delivered to Milton landfill site comprises of; transfer station waste, household waste, industrial and commercial and soils. The inputs to the site are predominately from transfer station which is delivered by road.
Operational hours are 07.00-16.30 Monday to Friday"
I read that as meaning out-of-hours access would have needed for the recycling lorry to go straight to landfill. And if there's security cameras at the site entrances, that would have been seen.
I think if SP thought the phone could have been in a recycling bin, other items could have been dumped in waste bins, hence holding off on use of the landfill.