Phone property results undefined, help!

class Pet {
   constructor(animal, age, breed, sound) {
     this.animal = animal;
     this.age = age;
     this.breed = breed;
     this.sound = sound;
    };

   get activity() {
     const today = new Date();
     const hour = today.getHours();

     if(hour > 8 && hour <= 20) {
      return 'playing';
    } else {
      return 'sleeping'; 
    }
   }

   get owner() {
     return this._owner;
   }

   set owner(owner) {
       this._owner = owner;
      console.log(`setter called: ${owner}`);
   }

   speak() {
     console.log(this.sound);
    };
}

class Owner {
  constructor (name, address) {
    this.name = name;
    this.address = address;
  }

  set phoneNumber(phone) {
    const phoneNormalized = phone.replace(/[^0-9]/g, '');
    this._phone = phoneNormalized;
  }

  get phone() {
    return this._phone;
  }

}

const ernie = new Pet('cat', 4, 'persa','miooou');
const vera = new Pet('dog', 8, 'border collie', 'woof woof');

ernie.owner = new Owner ('Naoki', 'Furogori 202');
ernie.owner.phone = '(090)4235-4545';

console.log(ernie.owner);