Hi Sitawach,
Thanks for contacting Apple Support Communities!
We understand that you're unable to access your Apple Music Family Subscription on your iPhone.
To start, we'd suggest that you check with the family organizer to determine if they have shared purchases enabled on their device so that you can access their subscriptions as outlined here: Add a family member to your subscriptions from Apple - Apple Support
"If you still can't share a subscription
After you set up Family Sharing, eligible subscriptions are automatically shared with your family members. If your family members can't access a subscription, here's what to do:
- If the subscription is an individual or student subscription, upgrade your subscription to a family plan.
- Subscriptions that aren't made by Apple, also called third-party subscriptions, might not be eligible to share. If a subscription is shareable, you see a Share with Family option when you go to Settings > [your name] > Subscriptions and tap the subscription."
If you're still unable to sign into Apple Music to enjoy the subscription, you can refresh your Media & Purchases settings by signing out, restarting your iPhone then sign back in again. You can go to Settings > [your name] > Media & Purchases > Sign Out. Once you've restarted your iPhone, you can follow the same path back to sign in to Media & Purchases and check your Apple Music app again.
If you're still unable to sign in, we'd suggest that you contact Apple directly to review your account with you. You can reach them here: Apple Support
We hope this helps.
Take care!