How can I stop SPAM emails syncing with my incoming mail?

[Windows Central Question]

I view my BTinternet mail using the email function on my Nokia Lumia 1020. It has worked perfectly fine until recently. I am now drowning in emails that normally stay in the SPAM folder in the BT account coming directly into the inbox on my phone. Can anyone help me with advice on how to stop this? The emails are in SPAM ok in the main BT email account, this only happens on my phone