Number 0808 501 5200 is potentially valid
Ofcom records show that numbers starting 0808501 are allocated to Vodafone Ltd (C&W). Note that due to number portability if an individual number has moved to a different operator this information is not publicly available.
Ofcom's last recorded change for this number range was June 2014.
The correct way to write the telephone number 08085015200 is 0808 501 5200
For more information on tariffs and usage of numbers starting 08 please visit the page on 08 numbers