Can someone access information that’s on my phone if they know my Apple password?

You should certainly make use of Apple's security options. Set a passcode on your phone and any other devices: this prevents someone getting into it to access your data, Do not forget the passcode: it cannot be retrieved if lost.

Set a passcode on iPhone - Apple Support

And if you haven't done so you should set up teo-factor authentication. If someone tries to get into your Apple ID from their own device they will need a code which is sent only to your 'trusted devices'.

Two-factor authentication for Apple ID - Apple Support

If they have your Apple ID and password they can certainly get access to anything you have in iCloud. They can make purchases on your account from iTunes and App Store. They could also lock you out of the account by changing the password. So if you think this has happened you’d better change the password immediately.

If they know your ID and passcode and you have not set up two-factor authentication they can log into your iCloud account online and see any synced data. This is why you should make sure your password is a strong one, and set up 2FA (see my post above).

The information is contained in the page I linked to above, and is at

https://support.apple.com/HT204915#setup