Can DMARC decrease the amount of spam and phishing I receive?

Yes it partially can, however you are not in control at this point.

If you receive very much spam and/or phishing, you should probably take a look at a great spamfilter or contact your ISP to help you with this.

DMARC is intended to reduce the amount of spam and phishing, however this is from the point of view of an email sender. Email senders can protect their domains against misuse as a phishing target.

If they implement DMARC they ask ISP’s to reject any invalid messages ‘from’ their domains. So if a bank (bank A) implements DMARC on their domain ‘this-is-bank-a.com’, you will no longer see phishing attacks with a ‘From’ domain of ‘this-is-bank-a.com’.

So you cannot implement DMARC ‘on your mailbox’, but this solution is on ‘domain level’.

How can DMARC decrease the number of phishing you receive? If more and more domain owners start to implement DMARC, it will eventually become a requirement for all emails. And this will decrease spam and phishing.