在input组件上绑定data-model="xxx" bindinput="inputWatch"，监听输入框输入：

<input placeholder="请输入6~12位密码" name="password" value="{{password}}" data-model="password" bindinput="inputWacth" type="password" maxlength="12" class="form-item-input"></input>

inputWacth: function (e) {
 let item = e.currentTarget.dataset.model;
 this.setData({
  [item]: e.detail.value
 });
}

当输入11位手机号后，验证码按钮变为可点状态；当3个输入框都有值时(密码大于等于6位，手机11位)，保存按钮变为可点状态。

<form bindsubmit="formPhone" wx:else>
 <view class="form-wrap">
  <view class="flex form-item">
  <view class="form-item-text">密码</view>
  <input placeholder="请输入6~12位密码" name="password" value="{{password}}" data-model="password" bindinput="inputWacth" type="password" maxlength="12" class="form-item-input"></input>
  </view>
  <view class="flex form-item">
  <view class="form-item-text">新手机</view>
  <input placeholder="请输入新手机号" name="account" value="{{account}}" data-model="account" bindinput="inputWacth" maxlength="11" type="number" class="form-item-input"></input>
  <button class="form-item-btn" catchtap="sendCode" data-account="{{account}}" disabled="{{codeDisabled}}">{{codeText}}</button>
  </view>
  <view class="flex form-item">
  <view class="form-item-text">验证码</view>
  <input placeholder="请输入验证码" name="verification" data-model="verification" bindinput="inputWacth" maxlength="6" class="form-item-input"></input>
  </view>
 </view>
 <view class="default-btn-wrap">
  <button class="default-btn" loading="{{loading}}" form-type="submit" disabled="{{disabled}}">保存</button>
 </view>
 </form>
var app = getApp();
var util = require('../../../utils/util.js');
var ck = require('../../../utils/check.js');
import { weChatUser } from '../../../utils/api.js'
Page({
 /**
 * 页面的初始数据
 */
 data: {
 codeText: '验证码', // 按钮文字
 disabled: true, // 
 codeDisabled: true,
 currentTime: 60,
 account: '', // 注册-账号
 password: '', // 注册-密码
 verification: '', // 验证码
 },
 // 修改手机号
 formPhone: util.throttle((e) => {
 let that = this,
  password = e.detail.value.password,
  account = e.detail.value.account,
  verification = e.detail.value.verification;
 // 判断手机号密码
 if (!ck.checkPhone(account) || !ck.checkNull(password, '密码') || !ck.checkNull(verification, '密码')) {
  return
 }
 // 手机号密码验证通过后，发请求修改密码
 let data = {
  "password": password,
  "phone": account,
  "verificationCode": Number(verification)
 }
 let result = weChatUser.updatePhoneBinding(data)
 result.then((res) => {
  if (res) {
  wx.showToast({
   title: '修改账号成功',
   mask: true
  })
  setTimeout(() => {
   wx.navigateBack({
   delta: 1
   })
  }, 2000)
  }
 })
 // 成功后，返回上一页
 }, 1000),
 // 发送修改手机号的验证码
 sendCode: util.throttle(function (e) {
 let account = e.currentTarget.dataset.account;
 // 判断手机号密码
 if (!ck.checkPhone(account)) {
  return
 }
 ck.countDown(this)
 var data = {
  phone: Number(account)
 }
 let result = weChatUser.getVerificationCode(data)
 result.then((res) => {
  if (res) {
  wx.showToast({
   title: '发送成功',
   icon: 'none',
   mask: true
  })
  }
 })
 }, 1000),
 // 监听 输入(控制按钮样式变化)
 inputWacth: function (e) {
 let item = e.currentTarget.dataset.model;
 this.setData({
  [item]: e.detail.value
 });
 let len = this.data.password.length;
 if (this.data.account && this.data.account.length === 11) {
  this.setData({
  codeDisabled: false
  })
  if (len >= 6 && this.data.verification) {
  this.setData({
   disabled: false
  })
  } else {
  this.setData({
   disabled: true
  })
  }
 }
 },
 /**
 * 生命周期函数--监听页面加载
 */
 onLoad: function (options) {
 wx.setNavigationBarTitle({
  title: options.title,
 })
 }
})
// check.js
function checkPhone(phone) {
 // 判断手机号
 if (!phone) {
 wx.showToast({
  title: '请输入手机号',
  icon: 'none',
  duration: 2000
 })
 return false
 }
 if (phone.length < 11) {
 wx.showToast({
  title: '手机号有误，请重新输入',
  icon: 'none',
  duration: 2000
 })
 return false
 }
 if (!(/^1[3456789]\d{9}$/.test(phone))) {
 wx.showToast({
  title: '手机号有误，请重新输入',
  icon: 'none',
  duration: 2000
 })
 return false
 }
 return true
}
function checkNull(val, msg) {
 if (!val) {
 wx.showToast({
  title: `请填写${msg}！`,
  icon: 'none'
 })
 return false
 }
 return true
}
function countDown(self) {
 let currentTime = self.data.currentTime;
 self.setData({
 codeText: currentTime + 's'
 })
 let interval = setInterval(function () {
 self.setData({
  codeText: (currentTime - 1) + 's'
 })
 currentTime--;
 if (currentTime <= 0) {
  clearInterval(interval)
  self.setData({
  codeText: '重新获取',
  currentTime: 60
  })
 }
 }, 1000)
}
module.exports = {
 checkPhone,
 checkNull,
 countDown
}
// util.js
// 防止多次重复点击（函数节流）
function throttle(fn, gapTime) {
 if (!gapTime) {
 gapTime = 1000;
 }
 let _lastTime = null;
 // 返回新函数
 return function(e) {
 let _nowTime = +new Date();
 if (_nowTime - _lastTime > gapTime || !_lastTime) {
  // fn(this, e); // 改变this和e
  fn.apply(this, arguments)
  _lastTime = _nowTime;
 }
 }
}
module.exports = {
 throttle
}